In a four-stroke cycle engine, power is recovered from the combustion process in four separate piston movements (strokes) of a single piston, including intake, compression, power, and exhaust strokes. During the intake stroke, the intake valve is opened to introduce air into the combustion chamber. Similarly, during the exhaust stroke, the exhaust valve is opened to allow exhaust to be released from the combustion chamber. During the compression and power strokes, the intake and exhaust valves are maintained closed, thus sealing the combustion chamber and maximizing compression during the compression stroke and efficiently transferring the energy resulting from combustion into piston movement in the power stroke. The exhaust gases flowing out of the cylinder via the exhaust valve include the by-products of combustion. Thus, over time, soot and other carbon materials may build up in the exhaust valve. As one example, the exhaust valve may become loaded with carbon buildup, which may in some examples cause the exhaust valve to exhibit degradation (e.g. stuck in at least a partially open position). If the combustion chamber is not sealed during the compression stroke, for example, a cylinder may lose most of its air/fuel mixture prior to ignition leading to combustion instability and misfire.
One example approach for conducting off-board cylinder leak test is shown by Sellers in U.S. Pat. No. 7,581,433. Sellers introduces an apparatus including a hose having an end configured for communication with a spark plug hole connecting to a cylinder to be tested and an end for attachment to a source of pressurized gas. Pressurized gas is routed into the cylinder and in-cylinder pressure is monitored to detect leaks in the cylinder.
However, the inventors herein have recognized potential issues with such systems. As one example, off-board diagnostic methods are required to be carried out by specialists, and it is additionally intrusive, difficult, and time consuming. The method described by Sellers may not be able to differentiate between a leak in the intake valve and a leak in the exhaust valve of the cylinder. A leak in the exhaust valve may adversely affect engine operation by causing misfires, backfires, rough idling, lower power output, and decreased fuel economy. If a cylinder is operated for a prolonged duration with a leaky exhaust valve, the high amount of heat released during combustion may further erode the valve.
In one example, the issues described above may be addressed by an engine method comprising: testing for degradation of an exhaust valve coupled to a cylinder of a multi cylinder engine, which drives a vehicle, by sealing the exhaust valve during an on-board test, routing compressed air into the cylinder during the test, and indicating presence or absence of degradation of the exhaust valve during the test based on an airflow through an exhaust coupled to the cylinders relative to a baseline airflow through the exhaust. In this way, by routing pressurized air through an engine cylinder during vehicle key-off conditions, it is possible to detect degradation of an exhaust valve coupled to the cylinder.
In one example, a diagnostic routine of a cylinder exhaust valve may be opportunistically carried out during vehicle key-off conditions when the engine is not operated. The vehicle may be an autonomous vehicle and/or a hybrid vehicle. The engine may be a boosted engine comprising a turbine driven intake air compressor and an electrically driven intake air compressor (herein also referred to as a battery operated electric booster) that is selectively operated for providing additional boost during increased torque demand. During on-board power distribution analysis, a cylinder may be identified to deliver a lower than threshold power. During an immediately subsequent vehicle key-off condition, the cylinder may be positioned with the intake valve open and the exhaust valve closed. The diagnostic routine for the exhaust valve includes, operating the electric booster to route pressurized air from the intake manifold to the exhaust manifold via the cylinder. Airflow exiting the cylinder may be compared to a threshold airflow and the exhaust valve may be diagnosed to be degraded based on a higher than threshold exhaust airflow. Subsequent engine cylinders of the multi cylinder engine may be similarly diagnosed to detect degradation of the respective exhaust valves.
In this way, by opportunistically using existing engine components, such as an electric booster and a differential pressure sensor, the need for off-board intervention and use of additional sensors and/or equipment for diagnostics of an exhaust valve may be reduced. The technical effect of carrying out diagnostics of the exhaust valve during vehicle key-off conditions is that the diagnostics of the exhaust valve may be carried out while maintaining the engine valves in a static position and without affecting engine performance. By identifying a cause for lower than threshold power output in a particular cylinder, suitable mitigating steps may be taken, thereby reducing the possibility of engine system degradation. Overall, by regularly monitoring the health of exhaust valves, combustion stability, engine performance, and fuel efficiency may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.